Heretofore, there have been systems in use in the field of power transmission, conversion, absorption or retardation which have proven to be somewhat efficient and successful in application such as land vehicle, aircraft launch and arresting systems or other mechanisms requiring controlled transfer and conversion of high torque or power.
Systems incorporating friction engaging means such as expending bands co-acting with rotary drum or rotating discs co-acting with pressure plates have been used in the past. However, they are burdened with many problems that are inconvenient, costly and in many cases impossible to contend with.
The most prominent problem involves the extreme heat from friction creating "hard spots" on the friction engaging surfaces resulting in excessive decrease in "slip" (gradual increase in energy transmission) efficiency which defeats the sole purpose of this type of device. Furthermore, the excessive heat and friction makes necessary frequent, costly and inconvenient refurbishment of friction engaging components. Excessive inertia against the drive means also becomes a problem owing to the inordinate size and weight of the components to be actuated in such systems.
As an alternative to friction systems, hydraulics or pump fluid systems avoid many of these problems, particularly in the areas of equipment wear and temperature regulation. The use of pump fluid pressure with lubricating properties through gear pump type systems as a speed and torque transmission means instead of co-acting friction members is obviously less damaging to working components as far as friction wear is concerned. The problems associated with "hard spots" in the friction type devices or distortion of components owing to extreme temperature fluctuations are also avoided with fluid systems which provide a dynamic and flexible medium to absorb the energy input and disperse the heat created, equally throughout the system or through heat exchanging facilities.
Hydrodynamic power absorbers or hydraulic torque converters equipped with heat exchanging facilities in the form of external cooling systems have recently been employed, for example, in land vehicles to provide smooth power transference from the motor or drive means to the drive wheel systems.
However, a problem plaguing these devices is that once engaged, they create constant pressure and motion of the transient fluid to sustain power transfer even after compatible speeds are reached between the drive means and the mechanisms to be driven. Therefore, although these devices have provided efficient operation or power transmission, they are limited by the capacities of the external cooling system which must be sufficiently capable, under continuous duty situations to sustain the viscosity of the pump fluid and prevent the distortion of working components due to excessive heat fluctuation. Furthermore, this mode of operation requires power of its own to operate in addition to the power required to attain the actual speed desired and is therefore inefficient in this respect.
Systems have been developed that incorporate synchronous cutout facilities or valves for suspending fluid flow once compatible speeds are reached between the drive means and the mechanism to be driven. These valve systems may be set to regulate the circulation of the pump fluid into or out of the gear pump pressure chamber to a reservoir or cooling system. In this way, pump fluid pressure and flow can be adjusted for operating at a predetermined power absorption level, and completely suspended once input drive and output mechanisms have reached compatible speeds. Although these devices provide some method of pump fluid control, there remain problems of extreme pressure and unacceptable stress on the external feed lines and control valve systems. These extraneous pressure problems restrict the ability to provide complete uninterrupted control of a full range of power and torque conversions or variations.